1. Field of the Invention
The invention relates to molding apparatus, and is concerned with the problem of molding, from polymerized resins, components having an axis of revolution, without drawing when stripping, which would be unacceptable for high precision components, often also of large size.
2. Description of the Prior Art
One solution to this manufacturing problem is already known from FR-A-2,613,662, which discloses molding apparatus which has to be heat-treated, the apparatus comprising a mold defined by a mold wall possessing a first thermal expansion coefficient, and a die for cooperating with the mold, the die having a wall with a second thermal expansion coefficient greater than the first thermal expansion coefficient. A molding operation using this appratus involves inserting the die into the mold at a first temperature, then heating the die and the mold to a second temperature above said first temperature, and subsequently cooling the die and the mold after the component has been formed in the mould.
However, this known apparatus is both complicated and costly. It is complicated in that the die is made up of expansible elements, surrounded by a form of envelope which is also extensible and which constitutes the molding member of the die. Making the unit is not easy, and the molding accuracy obtained is not always satisfactory.
The apparatus is also costly, not only because of the presence of the envelope, but also because of the rapid wear which occurs and which necessitates frequent replacement of expensive elements.